SUMMARY: The degradation of the foreign protein [C]methyl apohaemoglobin ([C-me]globin) was stimulated by ATP in cell-free extracts from exponential phase and shaken and standing stationary phase cells. A marked stimulation by ATP of the degradation of [C-me]globin was observed with exponential phase cell extracts which were preincubated for 30 min at 30 °C. Maximum stimulation was obtained with 3 mM-ATP and optimum degradation was at pH 8.0-8.5. Preincubation of extracts from both types of stationary phase cells did not affect the degree of ATP stimulation. The amount of ATP stimulation of [C-me]globin degradation by exponential phase extracts decreased markedly when the cells were starved in a growth limiting minimal medium before preparation of the cell extracts. In the exponential and both types of stationary phase extracts most of the activity was located in the cytoplasmic fractions. Although the periplasmic preparations contained a minor portion of the total activity, this activity showed a greater percentage stimulation by ATP. In the absence of ATP the specific proteolytic activities of the extracts from exponential and both types of stationary phase cells were similar. The proteolytic activities in all the cell extracts were inhibited to the same extent by phenylmethylsulphonyl fluoride, but the exponential and both types of stationary phase cell extracts were inhibited to different extents by EDTA and -hydroxymercuribenzoate. The results suggest that the proteolytic systems responsible for the degradation of abnormal proteins are different in exponential and stationary phase cells.


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